Heating and hot water supply system

ABSTRACT

A heating and hot water supply system is provided and includes at least a distribution unit, a hot water supply heat exchanger and a flow rate adjusting unit. The distribution unit adjusts a distribution ratio capable of handling operations including heating, hot water supply and simultaneous heating and hot water supply operations. When the hot water supply operation starts, first hot water supply control, which adjusting a temperature to a hot water supply set temperature by the flow rate adjusting unit, is performed. After supplying the hot water having the hot water supply set temperature according to the first hot water supply control is maintained for a reference time or longer, transition to second hot water supply control, which a tapping water temperature of the hot water supply heat exchanger is brought close to the hot water supply set temperature, and a mixing amount of clean water reduced, is performed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japanese Patent Application No. 2019-194383, filed on October 25. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND Technical Field

The disclosure relates to a heating and hot water supply system which has a heating operation function and performs a hot water supply operation using a heat medium for heating.

Description of Related Art

In recent years, in order to supply hot water at a hot water supply set temperature, water heaters that mix clean water with heated clean water, and supply hot water whose temperature is adjusted have been widely used. For example, in a water heater in Patent Document 1, in order to supply hot water at a hot water supply set temperature, a heating capacity of a burner is adjusted and thus the temperature of hot water heated by a heat exchanger is adjusted, and an amount of clean water mixed into the hot water is adjusted, and a hot water supply temperature is adjusted.

The clean water contains mineral components such as calcium, and as the amount of mineral components increases or as heating is performed and thus the temperature increases, the mineral components are likely to precipitate. Therefore, the mineral components may be precipitated as scale from the hot water heated by the heat exchanger, adhere to a hot water passage and narrow and block the passage.

In addition, in parts to which scale adheres, heat exchange is disturbed, and thus heat exchange efficiency decreases, the temperature increases, and in some cases, damage is caused. Therefore, in areas in which clean water in which scale is likely to precipitate is used, maintenance to remove scale in the water heater is performed regularly or according to the cumulative amount of hot water supply or the like. A Patent Documents, Japanese Patent No. 5200748, is provided for reference.

On the other hand, a heating and hot water supply system that performs a heating operation of heating a heat medium for heating and supplying it to an external heating terminal and a hot water supply operation of heating clean water in a heat exchanger for hot water supply using the heated heat medium and supplying hot water is also widely used. Also in such a heating and hot water supply system, when clean water containing a large amount of mineral components is heated, this is not preferable because scale precipitates in the heat exchanger for hot water supply and the heat exchange efficiency decreases, and there is also a risk of the hot water passage becoming blocked.

In particular, when the heating and hot water supply system has a configuration in which clean water is mixed into hot water heated by a hot water supply heat exchanger for hot water supply and hot water is supplied, since clean water is heated to a high temperature in the hot water supply heat exchanger, there is a problem of precipitation of scale being accelerated.

SUMMARY

The disclosure is to provide a heating and hot water supply system that can suppress precipitation of scale.

According to one embodiment of the disclosure, a heating and hot water supply system is provided and includes a combustion unit; a heat exchanger that heats a heat medium with combustion heat of the combustion unit; a heat medium circulation passage that connects the heat exchanger to an external heating terminal; a circulation pump that is disposed in the circulation passage; a bypass passage that branches from the circulation passage to bypass the external heating terminal; a hot water supply heat exchanger that is disposed in the bypass passage; a water supply passage through which clean water is supplied to the hot water supply heat exchanger; and a hot water supply passage through which hot water heated by the hot water supply heat exchanger is supplied. The heating and hot water supply system further includes a distribution unit that is provided at a branch section of the bypass passage, a hot water supply bypass passage that is branched from the water supply passage and connected to the hot water supply passage, and a flow rate adjusting unit that adjusts a bypass flow rate of the hot water supply bypass passage. The distribution unit is able to adjust a distribution ratio to be able to handle operations including a heating operation, a hot water supply operation, and a simultaneous heating and hot water supply operation, and wherein. When the hot water supply operation starts, a first hot water supply control, which adjusts to a hot water supply set temperature by adjusting the flow rate adjusting unit to mix the clean water with the hot water heated on the hot water supply heat exchanger, is performed. When supply of the hot water having the hot water supply set temperature according to the first hot water supply control has been maintained for a preset reference time or longer, transition to a second hot water supply control, which a tapping water temperature of the hot water heated by the hot water supply heat exchanger is brought close to the hot water supply set temperature, and the a mixing amount of the clean water is reduced, is performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a heating and hot water supply system according to an example of the disclosure.

FIG. 2 is a flowchart showing a hot water supply operation according to an example of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

Forms for implementing the disclosure will be described below with reference to examples.

A heating and hot water supply system 1 shown in FIG. 1 performs a heating operation of circulating a heat medium for heating heated using heat (combustion heat) of a combustion gas generated by a combustion part 7 (combustion unit) between it and an external heating terminal 2. In addition, the heating and hot water supply system 1 performs a hot water supply operation in which the temperature of clean water heated using heat of the heat medium is adjusted to a hot water supply set temperature and hot water is supplied. The heating and hot water supply system 1 can perform a simultaneous heating and hot water supply operation in which both a heating operation and a hot water supply operation are performed.

The heating and hot water supply system 1 includes the combustion part 7, a heat exchanger 8, a circulation passage 9 that connects the heat exchanger 8 to the external heating terminal 2, a circulation pump 10 provided upstream from the heat exchanger 8 of the circulation passage 9, a control unit 16 as a control part that controls a heating operation and the like. The circulation pump 10 causes the heat medium during combustion of the combustion part 7 to flow and be supplied to the heat exchanger 8.

In the combustion part 7, a combustion fan 7 a is driven, and air supply indicated by an arrow AS and a fuel gas indicated by an arrow F are mixed and supplied. An amount of combustion heat generated by combustion of the fuel gas in the combustion part 7 is adjusted by a rotational speed of the combustion fan 7 a. The heat exchanger 8 exchanges heat between the combustion gas generated by the combustion part 7 and the heat medium that flows through the circulation passage 9. In the heat exchanger 8, the heat medium is heated to a preset target heat medium temperature (for example, 85° C.). The combustion gas whose temperature is reduced due to heat exchange is exhausted to the outside as indicated by an arrow E.

In addition, the heating and hot water supply system 1 includes a bypass passage 11, a hot water supply heat exchanger 20 provided in the bypass passage 11, a water supply passage 19 connected to the hot water supply heat exchanger 20, and a hot water supply passage 21. The bypass passage 11 branches from the circulation passage 9 downstream from the heat exchanger 8 so that it bypasses the heating terminal 2 connected to the circulation passage 9, and is connected to the circulation passage 9 at a merging section C1 upstream from the circulation pump 10. Clean water indicated by an arrow CW is supplied from the water supply passage 19 to the hot water supply heat exchanger 20. Hot water heated by the hot water supply heat exchanger 20 is supplied from the hot water supply passage 21 to a hot water supply tap or the like as indicated by an arrow HW.

Next, the circulation passage 9 will be described.

In the circulation passage 9, a first temperature sensor 12 is disposed on the side (the side of the heating terminal 2) upstream from the merging section C1 with the bypass passage 11, a second temperature sensor 13 is disposed between the circulation pump 10 and the heat exchanger 8, and a third temperature sensor 14 is disposed downstream from the heat exchanger 8.

The first temperature sensor 12 detects the temperature of the heat medium used for heating that returns from the heating terminal 2 to the heat exchanger 8. The second temperature sensor 13 detects the temperature of the heat medium supplied to the heat exchanger 8. The third temperature sensor 14 detects the temperature of the heat medium heated by the heat exchanger 8. Based on the temperature detected using these temperature sensors, the combustion fan 7 a and the circulation pump 10 are controlled by the control unit 16 so that the temperature of the heated heat medium reaches the target heat medium temperature.

A first distribution valve 15 (distribution unit) is provided at a branch section between the circulation passage 9 and the bypass passage 11. The first distribution valve 15 can adjust a distribution ratio to be able to handle the heating operation, the hot water supply operation, and the simultaneous heating and hot water supply operation. The distribution ratio of the first distribution valve 15 is adjusted by the control unit 16.

The distribution ratio of the first distribution valve 15 is adjusted so that the heat medium is supplied only to the circulation passage 9 during the heating operation, and is adjusted so that the heat medium is supplied only to the bypass passage 11 during the hot water supply operation. In addition, during the simultaneous heating and hot water supply operation, the distribution ratio is adjusted so that hot water supply has priority, and the heat medium is supplied to the circulation passage 9 and the bypass passage 11 according to the distribution ratio.

The heat medium supplied to the circulation passage 9 is supplied to the external heating terminal 2 as indicated by an arrow HS. The heating heat medium supplied to the bypass passage 11 merges with the circulation passage 9 at the merging section C1. A supply passage for heat medium supply 18 as indicated by an arrow AF is connected between the circulation pump 10 and the first temperature sensor 12.

Next, the hot water supply heat exchanger 20, the water supply passage 19, and the hot water supply passage 21 will be described.

In the hot water supply heat exchanger 20, the clean water is heated by heat exchange between the heat medium of the bypass passage 11 and the clean water supplied from the water supply passage 19, and the heated hot water is supplied to the hot water supply passage 21. A hot water supply bypass passage 22 branches from the water supply passage 19, and a second distribution valve 23 that can adjust the distribution ratio is disposed at the branch section. The clean water supplied from the water supply passage 19 is distributed to the hot water supply heat exchanger 20 and the hot water supply bypass passage 22 by the second distribution valve 23. Therefore, the second distribution valve 23 serves as a flow rate adjusting unit that adjusts the bypass flow rate of the hot water supply bypass passage 22.

In the water supply passage 19, a flow rate adjusting valve 24, a flow rate sensor 25, and a water supply temperature sensor 26 are disposed upstream from the second distribution valve 23. The flow rate of the clean water supplied to the second distribution valve 23 can be adjusted by the flow rate adjusting valve 24. The flow rate sensor 25 detects a flow rate of clean water supplied to the second distribution valve 23, that is, a hot water supply flow rate. The water supply temperature sensor 26 detects a temperature (water supply temperature) of the clean water.

The hot water supply bypass passage 22 branches from the water supply passage 19 so that it bypasses the hot water supply heat exchanger 20 and is connected to the hot water supply passage 21 at a merging section C2. A tapping water temperature sensor 27 is disposed between the hot water supply heat exchanger 20 and the merging section C2 of the hot water supply passage 21. The tapping water temperature sensor 27 detects the temperature (tapping water temperature) of hot water heated by the hot water supply heat exchanger 20.

A hot water temperature sensor 28 is disposed downstream from the merging section C2 of the hot water supply passage 21. The hot water temperature sensor 28 detects the temperature of hot water (hot water supply temperature) whose temperature has been adjusted by mixing hot water heated by the hot water supply heat exchanger 20 with clean water of the hot water supply bypass passage 22. The control unit 16 controls a hot water supply operation so that the hot water supply temperature reaches the preset hot water supply set temperature.

Next, the control unit 16 will be described.

The control unit 16 receives detection signals of various sensors such as the first temperature sensor 12 connected via a communication line. Then, when the combustion fan 7 a, the circulation pump 10, the first distribution valve 15, the second distribution valve 23, and the like are controlled based on the received detection signal, respective operations such as a heating operation, a hot water supply operation, and a simultaneous heating and hot water supply operation are controlled.

An operation terminal 17 is connected to the control unit 16. The operation terminal 17 includes a display unit 17 a that can display information such as various temperatures and operation states, and a switch unit 17 b for performing a setting operation and the like. According to the operation of the operation terminal 17, the hot water supply set temperature, the target heat medium temperature, and the like are set, and the heating operation is started or stopped.

Next, the heating operation of the heating and hot water supply system 1 will be described.

When the heating operation is started, the control unit 16 adjusts the distribution ratio of the first distribution valve 15 so that combustion is performed in the combustion part 7 to generate a combustion gas, the circulation pump 10 is driven, and the heat medium is supplied only to the circulation passage 9. The heat medium is heated to the target heat medium temperature with combustion heat of the combustion part 7 in the heat exchanger 8. The heat medium is supplied to the heating terminal 2 and used for heating, and then returned to the heat exchanger 8 and heated again. When the heating operation is stopped, the control unit 16 performs a heating operation stop operation such as stopping combustion in the combustion part 7 and stopping the circulation pump 10.

Next, the hot water supply operation of the heating and hot water supply system 1 will be described with reference to a flowchart of FIG. 2. In FIG. 2, Si (i=1, 2, . . . ) represents a step.

When supply of hot water is started by opening the hot water supply tap or the like, and the flow rate sensor 25 detects a flow rate equal to or higher than the preset minimum operation flow rate, the hot water supply operation is started in S1, and the process proceeds to S2. Specifically, the distribution ratio of the first distribution valve 15 is adjusted so that combustion is performed in the combustion part 7, the circulation pump 10 is driven, the heat medium is supplied to only the bypass passage 11, and the heat medium is supplied to the hot water supply heat exchanger 20.

Next, in S2, the hot water supply operation is performed according to the first hot water supply control, and the process proceeds to S3. The control unit 16 receives the tapping water temperature detected by the tapping water temperature sensor 27 and the water supply temperature detected by the water supply temperature sensor 26. Then, in order to make the hot water supply temperature detected by the hot water temperature sensor 28 close to the hot water supply set temperature, the distribution ratio of the second distribution valve 23 is adjusted based on the received tapping water temperature and water supply temperature, and the mixing amount of clean water at the merging section C2 is adjusted. In this manner, in the first hot water supply control, when the mixing amount of clean water is adjusted, the hot water supply temperature is adjusted to the hot water supply set temperature and the hot water is supplied, and thus controllability of the hot water supply temperature is excellent.

In the first hot water supply control, the heat medium is heated to the target heat medium temperature with combustion heat in the heat exchanger 8. The heated heat medium is supplied to the hot water supply heat exchanger 20, and the clean water supplied from the water supply passage 19 to the hot water supply heat exchanger 20 is heated. The hot water heated by the hot water supply heat exchanger 20 is discharged to the hot water supply passage 21.

The tapping water temperature detected by the tapping water temperature sensor 27 is a temperature higher than the hot water supply set temperature. For example, when the water supply temperature is 20° C. and the target heat medium temperature is 85° C., the tapping water temperature is 50° C. or higher, and is higher than a hot water supply installation temperature of around 40° C., which is generally set in many cases. When the hot water supply set temperature is high, the amount of the heat medium supplied having a target heat medium temperature supplied to the hot water supply heat exchanger 20 is increased and thus the tapping water temperature is further increased.

Next, in S3, it is determined whether the hot water supply temperature has been maintained at the hot water supply set temperature for a reference time (for example, 10 seconds) or longer. It is determined whether the hot water supply temperature in the first hot water supply control is stable. For example, when a state in which a difference between the hot water supply temperature and the hot water supply set temperature is within +/−0.5° C. is maintained for a reference time or longer, Yes is determined. When Yes is determined, the process proceeds to S4, and when No is determined, the process proceeds to S6.

Next, in S4, transition to the hot water supply operation according to the second hot water supply control is performed, and the process proceeds to S5. In the second hot water supply control, in order to make the tapping water temperature of the hot water supply heat exchanger 20 close to the hot water supply set temperature, the amount of combustion heat generated by the combustion part 7 is adjusted, and the temperature of the heat medium made lower than the target heat medium temperature. When the temperature of the heat medium supplied to the hot water supply heat exchanger 20 decreases, the tapping water temperature approaches the hot water supply set temperature. In addition, according to drive control of the circulation pump 10, the flow rate of the heat medium supplied to the hot water supply heat exchanger 20 is reduced, and thus the tapping water temperature can approach the hot water supply set temperature. Since the tapping water temperature, that is, the temperature of hot water heated by the hot water supply heat exchanger 20, is lower than the temperature during the first hot water supply control, precipitation of scale in the hot water supply heat exchanger 20 is suppressed.

In addition to adjust the temperature or the flow rate of the heat medium, in order to set the mixing amount of clean water in according to the tapping water temperature, the distribution ratio of the second distribution valve 23 is adjusted, and the mixing amount of clean water is reduced. Here, the mixing amount of clean water during the second hot water supply control may be zero but it is preferable to mix in clean water even if the mixing amount is smaller than that during the first hot water supply control in order to control the hot water supply temperature.

Next, in S5, it is determined whether the hot water supply flow rate has changed. When the hot water supply flow rate detected by the flow rate sensor 25 during the second hot water supply control has changed and the determination is Yes, the process proceeds to S7, and when No is determined, the process returns to S4, and the second hot water supply control continues.

On the other hand, when No is determined in S3, it is determined whether the hot water supply flow rate has changed in S6. When the hot water supply flow rate detected by the flow rate sensor 25 during the first hot water supply control has changed and the determination is Yes, the process proceeds to S7, and when No is determined, the process returns to S2 and the first hot water supply control continues.

Next, in S7, it is determined whether change in the hot water supply flow rate has been caused by ending of hot water supply. For example, when the hot water supply tap or the like is blocked, and the flow rate sensor 25 no longer detects a flow rate equal to or higher than the minimum operation flow rate, the hot water supply has ended. When the hot water supply has ended and the determination is Yes, the process proceeds to S8, and when the hot water supply is continuing and the determination is No, the process returns to S2, and the hot water supply operation according to the first hot water supply control is performed.

When the hot water supply flow rate changes during the second hot water supply control, unless the hot water supply is completed, transition to the first hot water supply control is performed and the hot water supply operation continues. When the hot water supply flow rate changes during the first hot water supply control, unless the hot water supply is completed, the hot water supply operation according to the first hot water supply control continues. According to the first hot water supply control having excellent controllability of the hot water supply temperature, change in the hot water supply temperature due to change in the hot water supply flow rate is reduced.

Next, in S8, a hot water supply stop operation is performed and the hot water supply operation ends. In the hot water supply stop operation, for example, combustion in the combustion part 7 is stopped, driving of the circulation pump 10 is stopped, and a standby state is maintained until the next operation.

Next, the simultaneous heating and hot water supply operation of the heating and hot water supply system 1 will be described.

In the simultaneous heating and hot water supply operation, in order to perform the heating operation and the hot water supply operation at the same time, the heat medium heated to a target heat medium temperature is distributed to the circulation passage 9 and the bypass passage 11 by adjusting the distribution ratio of the first distribution valve 15. The distribution ratio of the first distribution valve 15 is adjusted so that the hot water supply operation has priority.

For example, when the heating operation is started during the hot water supply operation, the hot water supply operation in the first hot water supply control is performed and the heat medium is heated to a target heat medium temperature. If there is residual combustion heat that can be generated in the combustion part 7, the simultaneous heating and hot water supply operation is performed by adjusting the distribution ratio of the first distribution valve 15 so that the heat medium is also supplied to the heating terminal 2.

On the other hand, when the hot water supply operation is started during the heating operation, the distribution ratio of the first distribution valve 15 is adjusted, the heat medium heated to a target heat medium temperature is also supplied to the bypass passage 11, and transition to the simultaneous heating and hot water supply operation is performed. In this case, supply of hot water having a hot water supply set temperature according to the first hot water supply control has priority. In addition, the amount of combustion heat generated in the combustion part 7 increases so that the heat medium mixed in and used for heating and hot water supply can be heated to the target heat medium temperature.

Operations and effects of the heating and hot water supply system 1 in the above example will be described.

In the first hot water supply control, the clean water is mixed with the hot water heated to a temperature higher than the hot water supply set temperature, and the hot water supply is performed using the hot water whose temperature is adjusted. In addition, in the second hot water supply control, heating is performed so that the tapping water temperature of the hot water supply heat exchanger 20 is closer to the hot water supply set temperature than that of the first hot water supply control, and hot water supply is performed using a small amount of clean water mixed in in order to adjust the temperature. Then, when hot water supply starts, hot water supply in the first hot water supply control is performed and the hot water supply temperature is stable, and then transition to hot water supply in the second hot water supply control is performed. Accordingly, since the temperature of hot water heated by the hot water supply heat exchanger 20 decreases to a temperature close to the hot water supply set temperature, it is possible to suppress precipitation of scale from hot water.

When the hot water supply flow rate during hot water supply in the second hot water supply control changes, the hot water supply temperature changes. However, change in the hot water supply temperature can be reduced according to transition to hot water supply in the first hot water supply control. Therefore, it is possible to reduce inconvenience to a hot water user due to a change in the hot water supply temperature.

Other Configurations

According to one embodiment of the disclosure, a heating and hot water supply system is provided and includes a combustion unit; a heat exchanger that heats a heat medium with combustion heat of the combustion unit; a heat medium circulation passage that connects the heat exchanger to an external heating terminal; a circulation pump that is disposed in the circulation passage; a bypass passage that branches from the circulation passage to bypass the external heating terminal; a hot water supply heat exchanger that is disposed in the bypass passage; a water supply passage through which clean water is supplied to the hot water supply heat exchanger; and a hot water supply passage through which hot water heated by the hot water supply heat exchanger is supplied. The heating and hot water supply system further includes a distribution unit that is provided at a branch section of the bypass passage, a hot water supply bypass passage that is branched from the water supply passage and connected to the hot water supply passage, and a flow rate adjusting unit that adjusts a bypass flow rate of the hot water supply bypass passage. The distribution unit is able to adjust a distribution ratio to be able to handle operations including a heating operation, a hot water supply operation, and a simultaneous heating and hot water supply operation. When the hot water supply operation starts, a first hot water supply control, which adjusts to a hot water supply set temperature by adjusting the flow rate adjusting unit to mix clean water with the hot water heated by the hot water supply heat exchanger, is performed. When supply of hot water having the hot water supply set temperature according to the first hot water supply control has been maintained for a preset reference time or longer, transition to a second hot water supply control, which a tapping water temperature of the hot water heated by the hot water supply heat exchanger is brought close to the hot water supply set temperature and a mixing amount of the clean water is reduced, is performed.

According to the above configuration, in the first hot water supply control, the clean water is mixed with the hot water heated to a temperature higher than the hot water supply set temperature, and the hot water supply is performed using the hot water whose temperature is adjusted. In addition, in the second hot water supply control, the heating is performed so that the tapping water temperature of the hot water heated by the hot water supply heat exchanger is closer to the hot water supply set temperature than that of the first hot water supply control, and the hot water supply is performed using a smaller mixing amount of the clean water than that in the first hot water supply control. Then, when the hot water supply starts, the hot water supply in the first hot water supply control is performed, and the temperature of the hot water supply is stable, and then the transition to the hot water supply in the second hot water supply control is performed. Accordingly, since the temperature of the hot water heated by the hot water supply heat exchanger decreases to a temperature close to the hot water supply set temperature, it is possible to suppress precipitation of scale from the heated hot water.

In one embodiment of the disclosure, when the second hot water supply control is performed, if a hot water supply flow rate changes, transition to the first hot water supply control is performed.

According to the above configuration, when the hot water supply flow rate during the hot water supply in the second hot water supply control changes, the hot water supply temperature changes. However, change in the hot water supply temperature can be reduced by the transition to the hot water supply in the first hot water supply control. Therefore, it is possible to reduce inconvenience to a hot water user due to a change in the hot water supply temperature.

According to the heating and hot water supply system of the disclosure, it is possible to suppress precipitation of scale from hot water.

When the operation for starting the heating operation is performed during the hot water supply operation, since the hot water supply has priority, the heating operation may not be started until hot water supply is completed. In addition, those skilled in the art can implement forms in which various modifications are added to the above embodiment without departing from the spirit of the disclosure, and the disclosure includes such modifications.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents. 

What is claimed is:
 1. A heating and hot water supply system, comprising: a combustion unit; a heat exchanger that heats a heat medium with combustion heat of the combustion unit; a heat medium circulation passage that connects the heat exchanger to an external heating terminal; a circulation pump that is disposed in the circulation passage; a bypass passage that branches from the circulation passage to bypass the external heating terminal; a hot water supply heat exchanger that is disposed in the bypass passage; a water supply passage through which clean water is supplied to the hot water supply heat exchanger; and a hot water supply passage through which hot water heated by the hot water supply heat exchanger is supplied; a distribution unit that is provided at a branch section of the bypass passage; a hot water supply bypass passage that branches from the water supply passage and connected to the hot water supply passage; and a flow rate adjusting unit that adjusts a bypass flow rate of the hot water supply bypass passage, wherein the distribution unit is able to adjust a distribution ratio to be able to handle operations including a heating operation, a hot water supply operation, and a simultaneous heating and hot water supply operation, and when the hot water supply operation starts, a first hot water supply control, which adjusts to a hot water supply set temperature by adjusting the flow rate adjusting unit to mix the clean water with the hot water heated by the hot water supply heat exchanger, is performed, and when supply of the hot water having the hot water supply set temperature according to the first hot water supply control has been maintained for a preset reference time or longer, transition to a second hot water supply control, which a tapping water temperature of the hot water heated by the hot water supply heat exchanger is brought close to the hot water supply set temperature and a mixing amount of the clean water is reduced, is performed.
 2. The heating and hot water supply system according to claim 1, wherein, when the second hot water supply control is performed, if a hot water supply flow rate changes, transition to the first hot water supply control is performed. 